Thin film deposition process

ABSTRACT

Provided is a thin film deposition process that allows high-precision control of the in-plane distribution of a thin film being deposited on a substrate. The process is a process of depositing a thin film on a substrate in a chamber by atomic layer deposition (ALD) which includes repeating a deposition cycle to deposit the thin film on the substrate. The deposition cycle includes the steps of: feeding a reactive gas and a carrier gas to the chamber and feeding a source gas at a reduced concentration to the chamber to allow the source gas to adsorb on the substrate; feeding the reactive gas and the source gas to the chamber to allow the source gas to adsorb on the substrate; feeding the reactive gas and the carrier gas to the chamber to purge, from the chamber, the source gas not adsorbing on the substrate; applying RF power to the chamber to turn the reactive gas into a plasma so that the source gas activated by the plasma is allowed to come into contact with a surface of the substrate; and feeding the reactive gas and the carrier gas to the chamber to purge, from the chamber, the source gas remaining unreacted and the reactive gas.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Application No. 63/057,197, filed on Jul. 27, 2020 in the United States Patent and Trademark Office, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a thin film deposition process.

Related Art

An atomic layer deposition (ALD) process involves controlling the in-plane distribution of a thin film being deposited on a substrate such as a wafer. A method for controlling the in-plane distribution of a thin film includes adjusting parameters such as source input, gas flow rate ratio, RF power, and intervention by control of source purge time in chemical vapor deposition (CVD) process.

SUMMARY OF THE INVENTION

However, even if such parameters are adjusted, there is still difficulty in controlling the in-plane distribution of a thin film with a higher degree of precision. Therefore, a need exists for high-precision control of the in-plane distribution of a thin film being deposited on a substrate.

An aspect of the present disclosure is directed to a process of depositing a thin film on a substrate in a chamber by atomic layer deposition (ALD), the process including repeating a deposition cycle to deposit the thin film on the substrate. The deposition cycle includes the steps of: feeding a reactive gas and a carrier gas to the chamber and feeding a source gas at a reduced concentration to the chamber to allow the source gas to adsorb on the substrate; feeding the reactive gas and the source gas to the chamber to allow the source gas to adsorb on the substrate; feeding the reactive gas and the carrier gas to the chamber to purge, from the chamber, the source gas not adsorbing on the substrate; applying RF power to the chamber to turn the reactive gas into a plasma so that the source gas activated by the plasma is allowed to come into contact with a surface of the substrate; and feeding the reactive gas and the carrier gas to the chamber to purge, from the chamber, the source gas remaining unreacted and the reactive gas remaining unreacted.

The present invention allows high-precision control of the in-plane distribution of a thin film being deposited on a substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical cross-sectional view schematically showing a film deposition apparatus according to an embodiment;

FIG. 2 is a diagram showing ALD process sequences related to an embodiment;

FIG. 3A is a schematic diagram showing gas flow in a purge and source feed step;

FIG. 3B is a schematic diagram showing gas flow in a source gas feed step;

FIG. 3C is a schematic diagram showing gas flow in a purge step; and

FIG. 4 is a view showing results of measurement of thin films obtained by thin film deposition processes related to an embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, specific embodiments of the present invention will be described in detail with reference to the drawings. It will be understood that the embodiments below are not intended to limit the present invention and may be altered or modified in various ways without departing from the gist of the present invention.

<Film Deposition Apparatus>

While any type of film deposition apparatus may be used in the film deposition process according to an embodiment, a film deposition apparatus shown in FIG. 1 may be specifically used.

FIG. 1 is a vertical cross-sectional view schematically showing a film deposition apparatus 1 according to an embodiment. The film deposition apparatus 1 of FIG. 1 is configured to deposit a thin film on a substrate W such as a semiconductor wafer W by plasma enhanced atomic layer deposition (PEALD).

The film deposition apparatus 1 includes a top-opened and bottom-closed, substantially cylindrical chamber 10 and a table 12 which is provided in the chamber 10 and on which a substrate W is mounted.

The chamber 10 is electrically grounded through a grounding conductor (not shown). The chamber 10 has an inner wall, for example, whose surface is covered with a coating (not shown) made of a plasma-resistant material.

The table 12 is made of a metallic material such as an aluminum alloy. The bottom of the table 12 is supported by a support member 13 made of an electrically conductive material and is electrically connected. The support member 13 is electrically connected to the bottom surface of the chamber 10. Therefore, the table 12 is grounded through the chamber 10 and functions as a lower electrode, which is paired with a gas feeder 14 functioning as an upper electrode. The table 12 has a built-in heater (not shown), which is configured to heat the substrate Won the table 12 at a desired temperature.

In this apparatus, a distance D is provided between the table 12 functioning as a lower electrode and the gas feeder 14 functioning as an upper electrode. The distance D may be in a range where a plasma can be generated between the table 12 and the gas feeder 14, for example, in the range of 7 mm to 15 mm.

The lower portion of the support member 13 extends downward through an insertion hole 11 provided at the center of the bottom of the chamber 10. The support member 13 is vertically movable by means of a raising and lowering mechanism (not shown), which raises and lowers the table 12.

Below the table 12, plural support pins (not shown) are provided inside the chamber 10, and the table 12 has insertion holes (not shown) that are provided to receive the support pins. As the table 12 is lowered, the support pins pass through the insertion holes in the table 12 to support the substrate W with their upper ends so that the substrate W can be transferred to a transfer arm (not shown), which enters the chamber 10 from the outside.

Above the table 12, the gas feeder 14 is provided in parallel to and facing the table 12. In other words, the gas feeder 14 is disposed to face the substrate W mounted on the table 12. The gas feeder 14 is configured to feed process gases for the treatment of the substrate W. For example, the gas feeder 14 is made of an electrically conductive metal such as an aluminum alloy, which also functions as an upper electrode.

An upper circumferential portion of the gas feeder 14 is held by an annular support member 16. The support member 16 is made of an insulating material such as quartz. The gas feeder 14 and the chamber 10 are electrically isolated from each other. A heater (not shown) may also be provided on the upper surface of the gas feeder 14.

The gas feeder 14 is connected to a reactive gas feed source (not shown), a carrier gas feed source (not shown), and a reservoir 19 through gas feed lines L1, L2, L3, and L4 outside the chamber 1. A source gas, a reactive gas, and a carrier gas are fed to the gas feeder 14 and then introduced through gas feed holes 15 into the chamber 10 in a shower-like manner.

In an outer section of the film deposition apparatus 1, the gas feed lines L1, L2, L3, and L4 have valves V1, V2, V3, V4, and V5 and other components such as mass flow controllers (not shown), which allow control of conditions for feeding process gases, such as gas type, gas mixing ratio, and flow rate. Specifically, the gas feed line L1 has the valve V1, the gas feed line L2 has the valves V2 and V3, the gas feed line L3 has the valve V4, and the gas feed line L4 has the valve V5. The valves V3, V4, and V5 are also called the pass switch (PS) valve, the inlet valve, and the outlet valve, respectively.

The reservoir 19 contains a source gas precursor. The reservoir 19 is connected to the chamber 10 through the gas feed lines L2, L3, and L4. The gas feed line L2 is connected to the gas feed lines L3 and L4. The gas feed line L3 is connected to the gas feed line L4 through the reservoir 19. The gas feed line L3 is connected upstream of the valve V3 in the gas feed line L2. The gas feed line L4 is connected downstream of the valve V3 in the gas feed line L2. When only the carrier gas is fed, the valve V3 is opened while the valves V4 and V5 are closed, and the carrier gas is fed to the chamber 10 through the gas feed line L2 and the valve V3. When the carrier gas and the source gas are fed, the valve V3 is closed while the valves V4 and V5 are opened, and the carrier gas and the source gas are fed to the chamber 10 through the gas feed lines L2, L3, and L4 and the valves V4 and V5.

The gas feeder 14 also functions as an upper electrode. The gas feeder 14 is electrically connected to a high-frequency power source 17 through a matching box. The high-frequency power source 17 supplies high-frequency power for generation of a plasma. The high-frequency power source 17 is configured to output high-frequency power, for example, at a frequency of 100 kHz to 100 MHz. The matching box is provided to match the internal and load impedances of the high frequency power source. When a plasma is generated inside the chamber 10, the matching box functions to provide apparent matching between the internal and load impedances of the high frequency power source.

The chamber 10 is also connected to an exhaust system 18 configured to evacuate the interior of the chamber 10. When the exhaust system 18 is driven, the atmosphere in the chamber 10 is evacuated so that the pressure is reduced to a predetermined degree of vacuum.

The deposition apparatus 1 includes one or more controllers (not shown) that are programmed or configured to perform a deposition process. It will be understood by those skilled in the art that the controller or controllers are connected to components including the power source, a heating system, pumps, the chamber, the mass flow controllers, and the valves.

[Substrate Preparation]

For deposition of a thin film, first, a substrate W is introduced into the interior of the chamber 10 and mounted on the table 12. The substrate W may be, but not limited to, a silicon substrate or a germanium substrate. The substrate W may be introduced under vacuum into the interior of the chamber 10 using a load lock chamber (not shown) or other means.

The heater is used to heat the substrate Won the table 12. For example, the substrate W may be heated at a temperature in the range of 50 to 500° C. During heating, a carrier gas is fed into the chamber 10.

The carrier gas may be, for example, one or more selected from the group consisting of a helium (He) gas, an argon (Ar) gas, and a hydrogen (H₂) gas. During the feed, the pressure in the chamber 10 is typically at least 50 Pa or more, preferably 300 Pa or more and typically at most 1,300 Pa or less, preferably 1,000 Pa or less. While the carrier gas is fed, a reactive gas described later may also be fed.

[Deposition Cycle]

FIG. 2 is a diagram showing ALD process sequences related to an embodiment. The ALD process sequences in FIG. 2 include a conventional sequence (Current Sequence) and a sequence according to an embodiment (New Sequence).

The deposition cycle includes a purge and source feed step, a source gas feed step, a purge step, a plasma contact step, and a post purge step. The reactive gas and the carrier gas are continuously fed into the chamber 10 throughout the steps of the deposition cycle.

The deposition cycle may be repeated as many times as desired depending on the target film thickness, composition, and quality, although the repetition is not essential. The sequence according to an embodiment differs from the conventional sequence in particular in that it includes the purge and source feed step. Hereinafter, each step of the deposition cycle will be described in detail.

[Purge and Source Feed Step]

First, while a reactive gas and a carrier gas are fed to the chamber 10, a source gas is fed at a reduced concentration to the chamber 10. As a result, the source gas is allowed to adsorb on the substrate W. FIG. 3A is a schematic diagram showing the flow of gases in the purge and source feed step. As shown in FIG. 3A, the valve V1 is opened so that the reactive gas is fed to the chamber 10 through the gas feed line L1. The valves V2, V3, V4, and V5 are also opened so that the carrier gas is fed to the chamber 10 through the gas feed lines L2, L3, and L4. The source gas in the reservoir 19 is carried by the carrier gas, which flows through the gas feed line L3, and is fed to the chamber 10 through the gas feed lines L4 and L2.

In this step, since the valves V3, V4, and V5 are opened, the source gas is diluted with the carrier gas and then fed to the chamber 10. The diluted source gas being fed to the chamber 10 has a concentration lower than that of the source gas being fed in the source gas feed step described later.

In this step, the source gas may be a material used in plasma-excited atomic layer deposition (PEALD), preferably an aminosilane, more specifically one or more selected from the group consisting of bis(diethylamino)silane (BDEAS), diisopropylaminosilane (DIPAS), tetrakis(dimethylamino)silane (4DMAS), tris(dimethylamino)silane (3DMAS), bis(dimethylamino)silane (2DMAS), tetrakis(ethylmethylamino)silane (4EMAS), tris(ethylmethylamino)silane (3EMAS), bis(tert-butylamino)silane (BTBAS), and bis(ethylmethylamino)silane (BEMAS).

The reactive gas may be a gas capable of reacting with the source gas in the presence of a plasma of the gas component. More specifically, the reactive gas is preferably one or more selected from the group consisting of an oxygen (O₂) gas, a nitrous oxide (N₂O) gas, a carbon dioxide (CO₂) gas, a nitrogen (N₂) gas, and an ammonia (NH₃) gas.

The reactive gas being fed to the chamber 10 may have a flow rate of about 50 sccm or more, preferably at least 3,000 sccm or more and may have a flow rate of at most 10,000 sccm or less, preferably 6,000 sccm or less.

The carrier gas and the source gas being fed to the chamber 10 may have a flow rate of about 500 sccm or more, preferably at least 2,000 sccm or more and may have a flow rate of at most 10,000 sccm or less, preferably 5,000 sccm or less.

The source gas may be fed together with the carrier gas for a time period of, for example, 0.05 seconds or more, preferably at least 0.1 seconds or more and at most 10 seconds or less, preferably 5 seconds or less.

The purge and source feed step may be performed before or after the source gas feed step. The sequence according to an embodiment described above includes performing the purge and source feed step once and performing the source gas feed step once. Alternatively, the purge and source feed step and the source gas feed step may each be performed two or more times.

[Source Gas feed Step]

Next, the reactive gas and the source gas are fed into the chamber 10. FIG. 3B is a schematic diagram showing the flow of gases in the source gas feed step. As shown in FIG. 3B, the valve V1 is opened so that the reactive gas is fed to the chamber 10 through the gas feed line L1. The valves V2, V4, and V5 are also opened and the valve V3 is closed so that the source gas is fed to the chamber 10 through the gas feed lines L2 and L4. Switching between the purge and source feed step and the source gas feed step is generally performed by opening and closing the PS valve V3. As a result, the source gas is allowed to adsorb on the substrate W so that a layer of source gas molecules is formed on the surface of the substrate W.

The source gas being fed together with the carrier gas to the chamber 10 may have a flow rate of about 500 sccm or more, preferably at least 2,000 sccm or more and may have a flow rate of at most 10,000 sccm or less, preferably 5,000 sccm or less. The source gas may be fed together with the carrier gas for a time period of, for example, at least 0.05 seconds or more, preferably 0.1 seconds or more and at most 10 seconds or less, preferably 5 seconds or less. The optimal time period for which the source gas is fed may be selected based on the source gas type, the pressure in the chamber 10, and other conditions.

[Purge Step]

After the feeding of the source gas, the reactive gas and the carrier gas are fed to the chamber 10 so that the source gas not adsorbing on the substrate W is purged from the chamber 10. FIG. 3C is a schematic diagram showing the flow of gases in the purge step. As shown in the drawing 3C, the valve V1 is opened so that the reactive gas is fed to the chamber 10 through the gas feed line L1. The valves V2 and V3 are also opened and the valves V4 and V5 are closed so that the carrier gas is fed to chamber 10 through gas feed line L2.

The purge step makes it possible to obtain a smoother thin film because it reduces contamination of the thin film with the source gas remaining in the atmosphere. When the source gas not adsorbing on the substrate W is discharged in this way from the chamber 10, a smoother thin film can be obtained due to the reduction in contamination of the thin film with the source gas remaining in the atmosphere in the chamber 10. Specifically, the source gas may be purged at a rate for the starting of application of high-frequency power, so that the generation of a plasma described later and plasma-assisted deposition of a thin film can be performed smoothly.

[Plasma Contact Step]

Next, the reactive gas and the carrier gas are fed into the chamber 10, and a high-frequency power is applied to the gas feeder 14, so that the reactive gas component (a gas component capable of being activated by plasma generation) in the process gas is turned into a plasma. The reactive gas activated by plasma generation is allowed to come into contact with the surface of the substrate W, so that the reactive gas component is allowed to react with the source gas component adsorbing on the substrate W. This makes it possible to deposit a thin film with a uniform thickness on the surface even when the surface of the substrate W has a three-dimensional structure.

More specifically, when the reactive gas and the carrier gas are fed into the chamber 10, the step may include applying a high-frequency power to turn, into a plasma, a reactive gas component which includes one or both of the reactive gas and the carrier gas; and allowing the reactive gas component activated by the plasma generation to come into contact with the source gas component adsorbing on the substrate W so that the reactive gas component is allowed to react with the source gas component. This makes it possible to deposit a thin film with a uniform thickness on the surface of the substrate W

[Post Purge Step]

After a monolayer for a thin film is formed, a by-product generated during the reaction between the reactive gas component and the source gas component is discharged from the chamber. In this step, the by-product may be discharged from the chamber using means for feeding at least one of the reactive gas and the carrier gas into the chamber to purge the source gas component not adsorbing on the substrate, means for evacuating the chamber 10 to discharge the source gas component, or a combination thereof.

[Deposition of Thin Film with Desired Thickness]

The discharge of the by-product from the chamber 10 may be followed by repeating a cycle including: allowing the source gas component to adsorb on the substrate W; discharging an excess of the source gas component from the chamber 10; feeding, into the chamber 10, the process gases including the reactive gas; applying a high-frequency power to the gas feeder 14 so that the reactive gas component in the process gas is turned into a plasma and allowed to react with the source gas component to form a thin film; and discharging the by-product from the chamber. This makes it possible to deposit a thin film with a desired thickness on the substrate W. The resulting thin film may have a thickness of at least 0.0001 μm, which corresponds to the thickness of a monomolecular layer, and may have a thickness of at most 1 μm or less, preferably 0.1 μm or less.

In an embodiment, the resulting thin film may be, for example, a SiO₂ film, a SiN film, or a SiC film. The deposition of such a useful thin film by plasma enhanced atomic layer deposition (PEALD) allows production of semiconductor devices with higher quality and reliability.

EXAMPLES

Next, examples of the present invention will be described, which are not intended to limit the scope of the present invention. FIG. 4 is a view showing results of analysis of thin films obtained by thin film deposition processes related to an embodiment. The table of FIG. 4 shows results of GPC (growth per cycle) (A/cycle), uniformity range/average (%), center/edge ratio, and mapping of in-plane distribution on water (+/−0.25%) with different PS valve V3-closing times. FIG. 4 also shows the relationship between PS valve V3-closing time and center/edge ratio.

As mentioned above, the switching between the purge and source feed step and the source gas feed step can be generally performed by opening and closing the PS valve V3. In the examples, the purge and source feed step was performed, and then the PS valve V3 was closed to switch from the purge and source feed step to the source gas feed step.

FIG. 4 indicates that as the PS valve V3-closing time is delayed, namely, as the time period for which the purge and source feed step is performed is increased, GPC decreases, namely, the thickness of the atomic layer per cycle decreases.

FIG. 4 also indicates that as the PS valve V3-closing time is delayed, the uniformity range/average value (%) and the center/edge ratio both increase, and the difference in thin film thickness between the center and edge of the wafer increases.

In addition, the thin film deposition process according to an embodiment allows the in-plane distribution map on wafer to be controlled in units of +/−0.25% whereas the conventional process has difficultly in controlling the in-plane distribution map on wafer in units of +/−0.25%. As shown above, the in-plane distribution of the thin film was successfully controlled by controlling the PS valve V3-closing time on the order of milliseconds.

As described above, the thin film deposition process according to an embodiment includes a deposition cycle including a purge and source feed step that includes feeding a reactive gas and a carrier gas to the chamber 10 and feeding a source gas at a reduced concentration to the chamber 10 to allow the source gas to adsorb on the substrate W. When the source gas is diluted in this way, the source gas can be diluted for a desired period of time by taking advantage of the tendency of the source gas adsorption to be more likely to occur on a central area of the wafer (or the tendency of the source gas adsorption to be less likely to occur on a peripheral portion of the wafer). Therefore, the thin film deposition process according to an embodiment allows high-precision control of the in-plane distribution of a thin film being deposited on the wafer W.

The thin film deposition process according to an embodiment can eliminate the need to use the mode of intervention by unstable control of source purge time in chemical vapor deposition (CVD) process and makes it possible to produce a thin film with a desired in-plane distribution using an existing ALD system.

In addition, the thin film deposition process according to an embodiment controls the in-plane distribution of the thin film in an ALD atmosphere and therefore achieves a very stable process. Further, the thin film deposition process according to an embodiment can control the duration of the purge and source feed step and the duration of the source gas feed step, which makes it possible to more strictly control the in-plane distribution of the thin film.

While embodiments of the present invention have been described above, it will be understood that the embodiments are not intended to limit the present invention. It will also be understood that the advantageous effects shown in the embodiments are mere examples of the most advantageous effect of the present invention and are not intended to limit the advantageous effects of the present invention. 

What is claimed is:
 1. A process of depositing a thin film on a substrate in a chamber by atomic layer deposition (ALD), the process comprising repeating a deposition cycle to deposit the thin film on the substrate, the deposition cycle comprising the steps of: feeding a reactive gas and a carrier gas to the chamber and feeding a source gas at a reduced concentration to the chamber to allow the source gas to adsorb on the substrate; feeding the reactive gas and the source gas to the chamber to allow the source gas to adsorb onto the substrate; feeding the reactive gas and the carrier gas to the chamber to purge, from the chamber, the source gas not adsorbing on the substrate; applying RF power to the chamber to turn the reactive gas into a plasma so that the source gas activated by the plasma is allowed to come into contact with a surface of the substrate; and feeding the reactive gas and the carrier gas to the chamber to purge, from the chamber, the source gas remaining unreacted and the reactive gas remaining unreacted.
 2. The process according to claim 1, wherein the step of feeding a reactive gas and a carrier gas to the chamber and feeing a source gas at a reduced concentration to the chamber to allow the source gas to adsorb on the substrate is performed before the step of feeding the reactive gas and the source gas to the chamber to allow the source gas to adsorb on the substrate.
 3. The process according to claim 1, wherein the step of feeding a reactive gas and a carrier gas to the chamber and feeing a source gas at a reduced concentration to the chamber to allow the source gas to adsorb on the substrate is performed after the step of feeding the reactive gas and the source gas to the chamber to allow the source gas to adsorb on the substrate.
 4. The process according to claim 1, wherein the reactive gas is selected from the group consisting of an oxygen (O₂) gas, a nitrous oxide (N₂O) gas, a carbon dioxide (CO₂) gas, a nitrogen (N₂) gas, and an ammonia (NH₃) gas.
 5. The process according to claim 1, wherein the carrier gas is selected from the group consisting of a helium (He) gas, an argon (Ar) gas, and a hydrogen (H₂) gas.
 6. The process according to claim 1, wherein the source gas comprises an aminosilane.
 7. The process according to claim 1, wherein the thin film comprises a SiO₂ film, a SiN film, or a SiC film.
 8. The process according to claim 1, wherein the deposition cycle is repeated until a desired film thickness is reached. 